Fitbone vs Precice: Is There a Difference in Regenerate Healing?

Abstract

The use of intramedullary lengthening nails (ILN) is now an accepted limb reconstruction technique. The most popular motorised systems enable optimal conditions for lengthening, namely stability, sub-millimetre accurate lengthening or retraction and an avoidance of common complications associated with external fixators, such as pin site infections, muscle tethering and regenerate deformity or fracture.

The fitbone stainless steel implant utilises an electrical current transmitted by a subcutaneous antenna to drive the motor. The precise intramedullary system, made of titanium, is lengthened by a rotating magnet driven by an electronic remote controller. To prevent nail breakage or deformity, protected partial weight-bearing is initially advised and weight-bearing permitted when sufficient regenerate has formed in the distraction gap.

Purpose

The aim of our study was to evaluate and compare the regenerate formation following lengthening using two different motorised ILN.

Methods

A retrospective review identified 13 patients (13 nails) who underwent femoral lengthening using the fitbone and 14 patients (16 nails) lengthened with the precise. Patients were matched for age, sex, aetiology and length achieved.

Regenerate analysis was undertaken using the pixel ratio value (PVR), calculated on the radiographs when at the desired length, followed at 4, 8, and 12 weeks. The mean of the two highest ratio values were also assessed, as an indicator that full weight-bearing would be permitted. Complications were recorded in relation to bone, soft tissues and implant.

Results

Seven males and 6 females underwent 10 antegrade and 3 retrograde fitbone lengthening. Nine male and 5 female underwent 14 antegrade and one retrograde precise lengthening. The mean age at surgery was 36 years in both groups. Mean length in the fitbone group was 41.7, and 46.8 mm in the precise group. All except one fitbone patient reached the desired length (6 mm short). The regenerate fully consolidated in all patients.

There was no statistical difference between the PVR measurements of the cortices at any time interval. There was no difference seen in the time for full weight-bearing or a difference seen in the mean PVR measured at this particular time. There were complications seen in the fitbone group including bolt migration, premature consolidation, and soft tissue irritation from the antenna requiring early surgical removal. There were no complications recorded in the precise group.

Discussion

This study has demonstrated no difference between the regenerate formation following femoral lengthening, with either the fitbone or precise ILN. All patients had full bone consolidation and there was no difference seen in time to full weight-bearing following completion of lengthening. The rate of complications seen in the fitbone group may be explained by the learning curve of a new implant.

There are several limitations including a retrospective review of a small cohort of patients. However, we conclude that both implants successfully lengthen and form excellent regenerate bone. We would recommend that the choice of implant should not be determined by the potential regenerate formation.

How to cite this article

Calder P, Robertson A, Tissingh EK, et al. Fitbone vs Precice: Is There a Difference in Regenerate Healing? Strategies Trauma Limb Reconstr 2024;19(3):156–160.

Introduction

Since accepting Ilizarov's method of distraction osteogenesis, limb lengthening and deformity correction techniques have continued to develop.^1–3 Traditionally performed using external fixators, associated complications such as pin site infection, soft tissue tethering, poor regenerate healing, and regenerate deformity or fracture following frame removal remain a major issue.⁴ To reduce these common problems, attempts have been made to reduce fixator time, such as lengthening over a nail technique, lengthening and then nailing or lengthening and then plating.^5–7 The use of an intramedullary device was found to enhance regenerate consolidation and prevent fracture and deformity.^8,9 Further innovation has led to the introduction of intramedullary lengthening nails (ILN), obviating the need for the external fixators.

There are two main groups of ILNs, those that utilise a ratchet system requiring the patient to rotate the limb to gain length, and the more popular motorised versions including the fitbone (originally Wittenstein, Igersheim, Germany and currently Ortho fix, Inc. Lewisville, TX, USA) and the precise intramedullary limb lengthening system (ILLS, NuVasive Inc., San Diego, California).^10–15 These devices offer sub-millimetre control of distraction, and with the Precise nail, accurate uncomplicated retraction if required. The fitbone is a stainless-steel implant which has a gear and spindle system driven by an electrical current. The motor is attached to an antenna which is placed in the subcutaneous tissue. A high frequency electrical current is passed from an external transmitter through the skin, which results in axial movement. The precise ILLS are manufactured from a titanium alloy with an internal rare-earth magnet connected to a motor. A hand-held external remote controller incorporating two rotating magnets results in accurate sub-millimetre lengthening or retraction.

The manufacturers recommend limited weight-bearing through the limb during and after lengthening has been achieved until sufficient regenerate consolidation in the distraction gap. This is to prevent nail deformity or breakage. This limitation led to the development of a weight-bearing implant, the precise stryde lengthening nail (NuCasive Inc., San Diego, California). Made of Biodur 108 stainless steel alloy, which is estimated to be between 1.3 and 2.5 times stronger than the precise titanium nail, enabled full weight-bearing and the potential of simultaneous bilateral limb lengthening. Unfortunately, reported adverse outcomes resulted in a world-wide withdrawal.^16–19 This also led to a temporary suspension of the precise nail from December 2020, pending a new safety notice from the MHRA.²⁰

The preferred implant for lower limb lengthening at our institution was the precise nail, but following suspension the fitbone was used in appropriate cases. Anecdotally, there appeared to be better bone regenerate formed and faster consolidation seen on the postoperative radiographs in the patients using the fitbone implant. The aim of this study was to evaluate and compare the regenerate formation formed following either the fitbone or precise ILN, and any potential implant advantage, if present.²⁰

Methods

This study was subject to Research and Developmental Review (Reg. No: SE24.12). We performed a retrospective case-note review of 26 patients identified from a prospectively collected database. The patients either underwent femoral antegrade or retrograde lengthening utilizing either the fitbone or precise ILN between 2014 and 2023. Patients were matched by sex, age at surgery, aetiology of shortening and lengthening undertaken.

The implants were inserted by one of three experienced limb reconstruction surgeons, utilising an accepted technique.^15,21 Intramedullary reaming was undertaken using the recommended straight rigid reamers in the fitbone cases and using flexible reamers for the precise. The osteotomy was pre-drilled prior to reaming, to enable venting during the reaming process and also allow grafting of the osteotomy site from the reamed bone fragments. In cases with acute deformity correction, further reaming was performed after corticotomy. Following a latency period of 6 days, lengthening commenced at a rate of one third of a millimetre, three times per day, or twice per day in the cases of congenital short femur. Physiotherapy commenced on the first postoperative day, focusing on hip and knee range of motion. Patients were restricted to 20 kg of weight through the operated limb, as recommended by both manufacturers. During the lengthening period, patients were reviewed every two weeks with clinical assessment and radiographs. Once the desired length was achieved, patients remained partial weight-bearing until sufficient regenerate was seen to allow full weight-bearing with review every 4 weeks. Sufficient regenerate consisted of the formation of two cortices noted on the radiographs. Traditionally, the formation of three cortices has been used as an indicator to remove an external fixator. With the intramedullary support from the nail, compared to the concept of reinforced concrete, a decision has been made to accept the formation of two cortices with the addition of the nail to allow safe full weight-bearing.

Regenerate formation was assessed utilising the pixel value ratio (PVR) method.^22,23 This compares the pixel value of the regenerate to normal adjacent bone on a digital radiograph. The radiographs were assessed with the McKesson Enterprise Medical Imaging PACS release 12.3 (2017) system. The PVR calculations were recorded for the regenerate anterior, posterior, medial and lateral cortical areas utilising the region of interest (ROI) measurement tool where a larger measured value corresponds with an area of increased density (Fig. 1). The formula for calculation of the value is below.

Fig. 1.

Pixel ratio value measurement of the regenerate ROI, proximal and distal normal bone segments

The PVR values were recorded when the desired lengthening was achieved, and at the 4, 8, and 12-week review. A median PVR value was calculated from the two highest cortical values at the same time intervals. The time full-weight bearing was permitted was recorded and any complications involving the implant, soft-tissue or bone. Statistical analysis was undertaken using the Mann–Whitney U test to compare the two groups after the data did not achieve requirements for normality (Statistics Kingdom).²⁴

Results

Thirteen consecutive patients who underwent femoral lengthening (13 nails) using a fitbone were compared to 14 patients who had 16 femurs (two bilateral) lengthened using the precise ILLS. There were 16 males and 11 females with a mean age of 36 years (Range 16–64). Patients were matched for surgical indication that included congenital and syndromic deficiency, and both post-traumatic growth arrest or shortening, including the management of non-union (Table 1).

Table 1.

Demographics

	Fitbone	Precice
Male	7	9
Female	6	5
Age	Mean 36 years (16–60)	Mean 36 years (16–63)
Antegrade	10	15
Retrograde	3	1
Length	Mean 41.7 cms (16–70)	Mean 46.8 cms (25–75)
Aetiology
Trauma-short	3	4
Trauma-non-union	3	2
Trauma-growth arrest	1	2
Congenital/Syndromic	6	5
Short stature unknown origin		1
Weight bearing permitted
4 weeks post lengthening	9	12
8 weeks post lengthening	2	4
12 weeks post lengthening	2

The mean lengthening in the fitbone group was 41.7 cm (Range 16–70) and in the precise group 46.8 cm (Range 25–75). The desired length was achieved in all but one patient, within the fitbone group left with a residual 6 mm length discrepancy. All healed with full consolidation of regenerate requiring no additional intervention. Full weight-bearing was permitted in the fitbone group in nine patients at four weeks post lengthening, two patients at 8 weeks and two patients at 12 weeks. Twelve patients in the precise group commenced full-weight bearing at four weeks post lengthening and four at 8 weeks.

Complications in the fitbone group included failure to lengthen in two patients, one of whom went onto premature consolidation, requiring re-osteotomy with a Gigli saw. Subsequent lengthening was successful. A 6 mm discrepancy was accepted in the other patient. One patient required several extra lengthening episodes, the planned lengthening episodes were unsuccessfully demonstrated by a reduced distraction gap at routine follow-up. It should be noted that the desired length was eventually achieved. Locking bolt displacement occurred in three patients. Two required urgent surgery to replace the bolts, in one case the bolt was held in place with a small fragment plate secured over the bolt with uni-cortical screws. One of the bolts was noted to be deformed at the end of lengthening, but no intervention was needed. One receiver was removed following lengthening due to persistent soft tissue irritation and pain. There were no complications noted in the precise group.

The median PVRs for the anterior, posterior, medial and lateral cortices are listed in Table 2. There was no statistical difference recorded at any of the time points, demonstrating no overall difference between the rate of regenerate consolidation between the two implants. Furthermore, comparing the two highest cortical median values had no significant difference. The median value for two cortices when weight-bearing commenced was 0.92 (IQR 0.815–0.95) in the fitbone group and 0.875 (IQR 0.83–0.91) in the precise group, which again had no statistical difference (p = 0.3743).

Table 2.

Mean pixel value ratios

Time	Cortex	Fitbone	Precice	Mann–Whitney U Test
At cessation of lengthening	Anterior	0.685	0.66	p = 1
	Posterior	0.66	0.685	p = 0.9579
	Medial	0.83	0.775	p = 0.4039
	Lateral	0.79	0.66	p = 0.1666
	Median best two	0.84	0.785	p = 0.583
4 weeks post	Anterior	0.85	0.80	p = 0.5684
	Posterior	0.80	0.795	p = 0.6764
	Medial	0.84	0.87	p = 0.6605
	Lateral	0.84	0.75	p = 0.5242
	Median best two	0.90	0.875	p = 0.7254
8 weeks post	Anterior	0.805	0.82	p = 0.9059
	Posterior	0.805	0.86	p = 0.409
	Medial	0.95	0.91	p = 0.8591
	Lateral	0.715	0.77	p = 0.3763
	Median best two	0.945	0.94	p = 0.7675
12 weeks post	Anterior	0.93	0.89	p = 0.7672
	Posterior	0.94	0.96	p = 0.5094
	Medial	0.96	0.965	p = 0.3381
	Lateral	0.85	0.91	p = 0.1953
	Median best two	0.96	0.985	p = 0.1737
At weight bearing	Median best two	0.92	0.875	p = 0.3743

Discussion

This study demonstrates no statistical difference between the density of regenerate formed when comparing regenerate formed following the fitbone or precise ILN, analysed using the PVR.^22,23 The regenerate went on to heal in all cases. There was no statistical difference in time to weight-bearing between the two patient cohorts (p = 0.3743), with a similar PVR noted when combining the two highest values.

The production of bone utilising the tension stress effect on tissues was pioneered by Ilizarov.^1,2 The method highlighted the need for bone stability, osteotomy technique and a rate and rhythm of one quarter of a millimetre four times a day to produce the optimum bone regenerate and associated soft tissue elongation. This was achieved using the classic Ilizarov ring fixator, but with accepted complications associated with the pin tracts through soft tissue and vulnerable to regenerate.⁴ Following the introduction of ILN, there has been supportive evidence of both clinical and radio graphical superiority over traditional external fixators.^14,25,26 When assessing factors that influence bone consolidation, however, patient age has been shown to be the most important, with increasing healing rates and rate of complications in the older population.^15,27,28

The motorised ILN offer all the advantages over an external fixator. Namely, the stability of the implant within the intramedullary canal and the accuracy of submillimetre lengthening and ability to retract if needed. The implant can also remain for many months after the lengthening has been completed, to enable full regenerate consolidation and remodelling, which will protect against regenerate deformity and fracture following implant removal. Furthermore, in intramedullary lengthening the regenerate produced by the tension stress effect may be augmented by autograft from the reamings which are extruded at the osteotomy site if the drill holes of a DeBastiani style osteotomy are placed first, resulting in accelerated consolidation.

There are other potential factors that could contribute to faster regenerate consolidation. The manufacturers of the fitbone recommend the use of rigid straight reamers to enlarge the intramedullary canal. These reamers are sharp and anecdotally appear to produce more and larger bone reaming fragments. The lengthening osteotomy sites are pre-drilled to allow venting of the canal and enable seeding of the osteotomy with the bone reamings. This may therefore result in more seeding of the site using the rigid reamers, although this cannot be quantified in vivo. It is probable however given our results that although more bone may be visible initially, the finer ‘grind’ from flexible reamers, though less visible initially, has just as much osteogenic potential.

The fitbone motor is driven by electricity supplied by a subcutaneous antenna. The regenerate formation may be influenced by the electrical current. Choi et al. demonstrated in an animal model that an application of an electrical current during distraction led to an increase in bone formation.²⁹ The internal magnet of the precise nail rotates due to the magnetic field created by the two rotating magnets in the hand-held device. Henstock et al. showed that intracellular cascades of growth factors such as bone morphogenic protein 2 can be amplified by the use of magnets.³⁰ The relevance of these may be questioned, both in terms of the impact on bone regenerate formation during distraction osteogenesis and also how it may be possible to measure the influence from the electricity or magnetism.

There are several accepted limitations of this study. There are small numbers for comparison, and the fitbone cases represent the learning curve of the surgeons whose preference was previously to use the precise lengthening nail. This could account for the difference in complication rate. An attempt has been used to match the patient demographics and aetiology, but Table 1 shows that there are differences between the two groups which may have influenced outcome.

In conclusion, this study demonstrates no apparent difference between the two implants, fitbone and precise in relation to bone regenerate formation measured using a recognised assessment tool.^22,23 Both implants achieved the desired length with excellent regenerate consolidation. We would therefore not recommend the surgical choice of implant based on bone formation.

Orcid

Jonathan Wright https://orcid.org/0000-0001-6055-648X